Photographic material for the preparation of printing plates

ABSTRACT

A planographic printing plate is prepared from a photographic sheet material comprising a support, a light-sensitive silver halide emulsion layer and an exterior hydrophilic colloid stratum having at its free surface a pattern of finely divided silver particles, by contacting the same with an aqueous alkaline fixer composition containing an oxidizing agent for metallic silver and an organic thione, or mercapto tautomer thereof, for converting the pattern of silver particles into a hydrophobic ink-receptive pattern, the colloid stratum being hardened before the material is used for printing and preferably before or at least concurrently with its contact with said fixer composition, the extent of the hardening being at least that necessary to prevent removal of the colloid material during printing. The pattern of silver particles is produced by means of the silver complex diffusion transfer process in which insoluble development nuclei are applied to the free layer surface either from the diffusion transfer developing liquid or a separate liquid applied prior to the developing liquid. Preferably the colloid stratum is hardened by means of a latent hardener released during the course of the diffusion transfer process. The colloid stratum can be an external stratum of the emulsion layer or a separate colloid layer applied to the emulsion layer.

United States Patent De Haes et al.

1 1] 3,721,559 1March 20,1973

PREPARATION OF PRINTING PLATES [75] Inventors: Louis Maria De Haes; HugoKarel Gevers, both of Edegern; Johannes Josephus Vanheertum,l-lalle-Zandhoven, all of Belgium I [73] Assignee: Ag fa Gevaert N.V.,M0rtsel, Belgi- [22] Filed: Aug. 23, 1971 [21] Appl.No.: 174,140

. Related [1.8. Application Data [63] Continuation of Ser. No. 738,097,June 19, 1968,

abandoned.

[30] l I Foreign Application Priority Data June 19, 1967 GreatBritain..'. ..28,237/67 April 26, 1968 Great Britain ..l9,887/68 [52]U,S.'Cl. ..,....96/33, 96/29, 96/48, 97/76 51] Int. Cl .....G03f 7/02[58] Field of Search ..96/33, 29, 48, 76

[56] References Cited UNITED STATES PATENTS 3,490,905 7/l970 Blake"96/33 3,083,097 3/1963 Lassig et al ..96/ 29 2,725,298 11/1955Yutzyetalm, .....96/ 76 2,843,485 7/1958 Yutzy et al. ..96/29PHOTOGRAPHIC MATERIAL FOR THE.

Primary Examiner-J. Travis Brown Assistant Examiner-Edward C. KimlinAttorney-William J. Daniel [57] ABSTRACT A planographic printing plateis prepared from a photographic sheet material comprising a support, alight-sensitive silver halide emulsion layer and an exterior hydrophiliccolloid stratum having at its free surface a pattern of finely dividedsilver particles, by contacting the same with an aqueous alkaline fixercomposition containing an oxidizing agent for metallic silver and anorganic thione, or mercapto tautomer thereof, for converting the patternof silver particles into a hydrophobic ink-receptive pattern, thecolloid stratum being hardened beforethe material is used for printingand preferably before or at least concurrently with its contact withsaid fixer composition, the extent of the hardening being at least thatnecessary to prevent removal of the colloid material during print ing.The pattern of silver particles is produced by means of the silvercomplex diffusion transfer process in which insoluble development nucleiare applied to the free layer surface either from the diffusion transferdeveloping liquid or a separate liquid applied prior to the developingliquid. Preferably the colloid stratum is hardened by means of a latenthardener released during the course of the diffusion transfer process.The

'colloid stratum can be an external stratum of the emulsion layer or aseparate colloid layer applied to the emulsion layer.

12 Claims, No Drawings PI-IOTOGRAPIIIC MATERIAL FOR THE PREPARATION OFPRINTING PLATES This application is a continuation of Ser. No.

738,097, filed 6/19/68, and now abandoned.

.stances for promoting the silver deposition from the diffusingcomplexed silver halide, further on called development nuclei, at thesurface of the material, the development nuclei being present either ontop of the said emulsion layer or on top of a hardenable hydrophiliccolloid layer applied to said emulsion layer.

The diffusion transfer silver image produced in the photographicmaterial according to the present invention is substantially situated atthe surface of the material. According to a preferred embodiment of thisinvention a planographic printing plate can be prepared very simply fromthe diffusion transfer copy obtained by one single treatment as will bedescribed detailedly hereinafter.

The support sheet of the photographic material according to theinvention maybe any usual flexible support sheet, e.g., a paper sheet ora transparent hydrophobic usual film support such as a support ofcellulose triacetate or of a polyester, e.g., polyethyleneterephthalate.

Any silver halide emulsion of the negative or direct positive typepreferably a gelatin silver halide emulsion, may be used dependent onthe nature of the original to be reproduced. Preferably, however,emulsions of the negative type having a rather high sensibitiy of theorder as normally required for camera exposure are used. As a matter offact, although the exposure of the silver halide emulsion layer can becarried out according to any usual technique, e.g., in contact,reflectographically, by transmission or episco'pically, mostly anepiscopic exposure in a camera is carried out. The silver halideemulsion layer preferably has a sensitivity of the order as normallyrequired for camera exposure. The silver halide emulsion layer generallycomprises an amount of silver halide equivalent to from about 0.5 g toabout 1.5 g of silver nitrate and preferably amounting only to theequivalent of about 1 g of silver nitrate. This means a considerableeconomy of silver halide with respect to the silver halide content ofemulsion layers commonly used in the production of diffusion transfercopies. If necessary a suitable subbing layer is provided for stronglyadhering the silverhalide emulsion layer to the support sheet.

The development nuclei may be provided directly on top of the silverhalide emulsion layer. In that case it should be a hardenable one andpreferably a gelatin silver halide emulsion layer. Preferably, however,one and sometimes even more other water-permeable layer(s) is (are)applied on top of the silver halide emulsion layer, the outer layeralways being a hardenable hydrophilic colloid layer preferably a gelatinlayer, on which the development nuclei have to be present.

According to a preferred embodiment the development nuclei are appliedon top of the photographic material at the preparation stage by means ofa specific after-treatment of the material with a liquid compositioncontaining such nuclei. In order to keep the development nuclei indispersion a minor amount of a hydrophilic protective colloid, e.g.,gelatin, may be added to the dispersion. This amount of colloid does notsuffice to form a layer and in most cases .is hardened at the hardeningstage'of the hydrophilic colloid layer or by diffusion of hardener fromsaid layer.

The development nuclei may also be supplied by a specific processingliquid with which the photographic material is wetted after theimage-wise exposure and before the alkaline processing liquid forcarrying out the diffusion transfer image formation is applied, or theymay be incorporated into the said alkaline processing liquid itself.

Suitable development nuclei for being applied to the photographicmaterial according to the present invention are sulphides of heavymetals such as the sulphides, of antimony, bismuth, cadmium, cobalt,lead, nickel, silver and zinc. Other suitable salts are the selenides,polysulphides, polyselenides, mercaptans and tin(ll)halides. Heavymetals or their salts and fogged silver halides are suitabletoo. Thecomplexed salts of lead and zinc sulphides are active alone as wellasmixed with thioacetamide, dithiobiuret, and dithiooxamide. Heavy metals,preferably silver, gold, platina, palladium, and mercury may be used intheir colloidal form. From these metals the noble metals are the mostactive ones. Thedevelopment nuclei may be applied on top of thephotographic material at the preparation stage or they may beincorporated into a processing liquid in the usual concentrations asgenerally known in the art. a I

For the preparation of the hydrophilic colloid outer layer anyhardenable hydrophilic colloid is suitable. Although gelatin is favored,as already mentioned above, other hardenable hydrophilic colloids suchas polyvinyl alcohol, casein, carboxymethylcellulose and sodium alginatecan be used too. If gelatin is used for forming the hydrophilic colloidouter layer, it may be submitted to a treatment as described in theUnited Kingdom Pat. specification No. 883,843 filed Sept. 2,

' 1959 by Agfa AG in order to improve the printing characteristics ofthe planographic printing plate.

The outer hydrophilic colloid layer, i.e., the silver halide emulsionlayer or an outer layer on top thereof, has to be hardened at theprinting stage.

Hardening of the hydrophilic colloid binder of the outer layer may occurbefore, during or after the treatment of the diffusion transfer copyproduced with the fixer composition for preparing the planographicprinting plate and must occur at least to such an extent that nosubstantial amount of colloid is transferred on printing neither to therollers for applying water and ink to the printing plate nor to thematerial to be printed. In other words hardening, i.e., insolubilizingin water and strengthening against mechanical damage must occur at leastto such an extent that the material obtained can be used as aplanographic printing plate. This explanation in our opinion willsuffice for one skilled in the art.

The said hardening mostly occurs before the said treatment with fixer.In that case the said hardening may occur by addition of the generallyknown hardening agents for gelatin and similar colloids such asfordevelopment nuclei in dispersion is applied on top of the said outerlayer the hardeners can also be incorporated-into said coatingcomposition. Hardening of the hydrophilic colloid binder of the outerlayer may also occur during the production of the diffusion transfersilver pattern by incorporating hardeners into at least one of theprocessing liquids and/or by incorporating latent hardeners into thephotographic materi-- al to be hardened. These latent hardeners areactive only in a well defined pH-range, mostly the pH-range of the usualalkaline processing liquid for carrying out the diffusion transfer imageformation. For more details on the useof latent hardeners inphotographic material there can be referred to United Kingdom Pat.specification No. 962,483 filed Jan. 1, 1962 by Agfa AG and German Pat.specification No. 1,203,604 filed Jan. 15, 1964 by Agfa AG. Finallyhardening of the outer hydrophilic colloid layer may also occur afterthe production of the silver pattern, viz. by treatment with a hardeningliquid. This liquid may be an aqueous hardening composition appliedbefore the treatment with the fixer, the fixer composition itself or anaqueous hardening composition applied after the treatment with thefixer.

' The exposure latitude of the photographic material according to thepresent invention in most cases can be prolonged considerably. Also theimage sharpness of the silver pattern can be increased and, as aconsequence thereof, the sharpness of the final result of printing canbe improved by applying antihalation dyes or pigments. These dyes or.pigments may be present in the .silver halide emulsion layer or in thesupport, but preferably are incorporated into a layer situated betweenthe silver halide emulsion layerand the support. If a transparentsupport is used the antihalation dyes or pigments may be applied to therear side of the material or on top of the emulsion layer dependent onthe manner inwhich the exposure is carried out, viz. atv

the front side or through the support. Preferably a red or blackantihalation dye or pigment is used. If the antihalation layer is graythe correctness of the exposure can easily be controlled 1 by judgingthe diffusion transfer image in transmittance before carrying out thefixing step.

The photographlcmaterial according to the present invention may compriseat least partof the compounds that are essential or useful for carryingout the diffusion transfer image formation such as developing. agents,preservatives for these developing agents, complexing agents,stabilizers, alkaline substances, black-toning agents, hardeners andsoftening agents in the materials used, whereby the aqueous processingliquid can be reduced to an aqueous solution of alkaline substancesdescribed in the United Kingdom Pat. specification No. 1,013,343 filedDec. 29, 1961 by Gevaert Photo Producten N.V.. For silver complexdiffusion transfer processes in which the developing agents andpreservatives for these developing agents are incorporated into thelight-sensitive and/or image-receiving material, there can be referredto United Kingdom Pat. specifications Nos. 1,000,115 filed Aug. 4, 1961,1,012,476 filed Dec. 18, 1961, 1,042,477 filed June 17, 1963, 1,054,253filed Aug. 6, 1963, 1,057,273 filed Feb. 3,

1964 and 1,093,177 filed Dec. 16, 1964 all by Gevaert Photo-ProductenN.V. I

It is a preferred embodiment of the present invention to incorporate atleast part and preferably even the total amount of developing agent(s),mostly hydroquinone and a 3-pyrazolidinone developing compound usedtogether, into the photographic material whereby the developing liquidbecomes reduced to an aqueous alkaline liquid that is substantially freefrom developing agent(s) and consequently shows excellent keepingqualities.

The presence of certain hydrophilic colloid binders,

e.g., carboxymethylcellulose, gum arabic, sodium alginate, propyleneglycol ester of alginic acid, hydroxyethyl starch, dextrine,hydroxyethylcellulose, polyvinylpyrrolidone, polystyrene sulphonic acidand polyvinyl alcohol in the outer hydrophilic colloid layer of thephotographic material often improves the hydrophilic, ink-repellentproperties of the non-printing areas of the printing plate finallyobtained. Also hygroscopic substances, likewise called hydrophilicsoftening agents, e.g. sorbitol, glycerol,trihydroxyethyl ether ofglycerol and turkish red oil, and certain wetting agents,

i.e., those mentioned hereinafter incorporated in atleast onehydrophilic colloid layer will improve the hydrophilic properties of thenon-printing areas.

The hydrophilic colloid outer layer also may advantageously comprise aconsiderable amount of pigment particles that will prevent the so-calledscumming (i.e., ink-acceptance that arises in the non-printing areas ofthe printing plate after a certain number of copies has been printed).The usual inorganic pigments, e.g., barium sulphate, titanium dioxide,china clay and silica applied from a colloidal solution, have proved tobe particularly suitable for this purpose. The pigment particles aregenerally homogeneously applied in such an amount that about 5-20 gthereof are present per sq.m. of the hydrophilic colloid outer layer. Asimilar anti-scumming effect may also be obtained by addingat least onemern'ber selected of colloidal silica, an inorganic acid, e.g.,o-phosphoric acid, a hydrophilic softening agentas those mentioned aboveand a suitable wetting agent to the fountain solution used during theprinting process. Suitable wetting agents are,

;-(C :)1 r- )s 'sodium dodecylsulphatesodium tetradecylsulphatev R--CH,SO,Na wherein R represents an alkyl group comprising from 14 to 18carbon atoms R hexadecyl 90 percent octadecyl 6 percent octadecenyl 4percent A very suitable fountain solution comprises water, glycerol,o-phosphoric acid and colloidal silica. v

For the production of the diffusion transfer silver image on top of thephotographic material according to the present invention, the materialis first image-wise exposed to an original. This may occur according toany usual technique as detailedly described above. The material is thentreated with an aqueous alkaline processing liquid for carrying out thediffusion transfer image formation in the presence of a developingagent, a complexing agent for silver halide and development nuclei ontop of the outer hardenable hydrophilic colloid layer. The said aqueousalkaline processing liquid may be applied in different ways, e.g., byspraying, by rubbing, with a lick roller, or by dipping the photographicmaterial in the liquid composition. In order to obtain a diffusiontransfer silver deposition that will be sufficiently dense, thephotographic material has to be kept for a short while, e.g., for about10 seconds, in the dark afterit has been wetted with the alkalineprocessing liquid for carrying out the diffusion transfer imageformation. The application of the fixer composition may already takeplace during the period the multilayermaterial is kept in the dark.However, this application of fixer may also occur thereafter.

For the production of the diffusion transfer silver image thephotographic material comprising development nuclei on top of the silverhalide emulsion layermay be provided in roller form. After image-wiseexposure, e.g., an episcopic exposure in a camera or an exposure througha transparent original in contact with the photographic material, thelatter may be guided automatically through a usual processing unitcontaining the alkaline processing liquid and comprising guiding anddriving means as generally known in the art. In order to overcomeprocessing irregularities during the cutting stage of the multilayermaterial, an empty tray with loose roller, which is lifted by thematerial during cutting, may be provided between the exposure unit andthe processing unit.

The production of a planographic printing plate from the photographicmaterial carrying at its surface a diffusion transfer silver pattern mayoccur according to any technique for producing a planographic printingplate from a sheet material having'a hardenable hydrophilic colloidouter layer carrying at its surface a pattern of silver particles. Inthis respect reference is made to German Pat. specifications Nos.1,011,280 filed Apr. l8, l956, 1,058,844 filed Apr. 27, 1957, 1,064,343filed Aug. 16, 1957, 1,128,296 filed Apr. 22,

1959 and 1,146,367 filed Apr. 22, 1959a" by Agfa AG. A specifictechnique especially suitable for being applied in order to convert thediffusion transfer copy produced from a photographic material accordingto the present invention into a planographic printing plate andaccording to which only one treatment (fixing) has to be carried out formaking the plate ready for printing will be described in detailhereinafter.

According to this preferred technique the photographic material carryingthe diffusion transfer silver image at its surface is treated with afixer being an aqueous treating composition buffered at a pH value from7 to 12 and to which have been added potassium cyanoferrateflll) and anorganic compound that converts the pattern of silver particles in ahydrophobic ink-receptive pattern.

Potassium cyanoferrateglll) mostly is incorporated into the fixer in aconcentration of from 25 to 300 g'per liter and may simply be added bydissolving it in the aqueous fixer composition. The effect of thepresent invention may also be obtained by using other generally knownoxidizing agents for silver particles instead of potassiumcyanoferrateflll) even by using such agents that only in a very minoramount produce silver ions at the surface of the silver pattern such aswater-soluble cadmium, strontium or calcium salts. However, the goodresults obtained by using potassium cyanoferrate(III) as an oxidizingagent cannot be obtained by using other oxidizing agents. This is veryunexpected since there exist many oxidizing agents having a betteroxidizing power than potassium cyanoferrate(IlI).

In addition to the potassium cyanoferrate(III) an organic compound thatconverts the silverimage parts in hydrophobic ink-receptive parts isadded to the fixer.

Examples of such organic compounds that have proved to be especiallysuitable for this purpose are thioxo compounds, including the tautomericstructures thereof, making the silver image ink-receptive, e.g.

- imidazoline-Z-thiones and imidazolidine-Z-thiones including theN-substit'uted derivatives such as imidazolidine-4-on-2-thionesincluding substituted derivatives such as phenyltetrazoline-thionesincluding derivatives such as tetrahydro pyrimidine-Z-thiones includingsubstituted derivatives such as tetrahydroand -dihydro-oxazine-2-thiones and thiazine-Z-thiones including substituted derivatives suchas l,3,4-dihydro thiadiazine-Z-thiones including sub- ,7

stituted derivatives such as thiourea compounds including substitutedderivatives preferably N-phenyl thiourea compounds such (ll) CH: S

(12)}. Nos

substituted The compounds that convert the silver image parts inhydrophobic ink-receptive parts may be added directly to the fixer, butare often added from an aqueous alkaline solution or from a solution ina suitable organic, water-miscible solvent such as ethanol, isopropanol,

ethylene glycolmonomethyl ether and dimethylformamide. They must be atleastpartially soluble in the fixer composition. They are mostly appliedin an' amount of from 0.5to 5 g per liter of fixer. it is remarkablethat most of the suitable compounds for converting the silver imageparts in ink-receptive parts are black-toning agents generally known inthe silver complex diffusion transfer process. A

An explanation of the reaction mechanism according to which the silverimage parts are converted into hydrophobic ink-receptive parts cannot begiven with certainty. Indeed, it might be a chemical transformation thattakes place or more likely a physical adsorption to the silver imageparts. In any event the fact remains that at least a superficialoxidation of the silver pattern is necessary. With certain thioxocompounds it is possible that oxidation products of these compounds arepresent in the fixer and it is not beyond possibility that preciselythese oxidation products are responsible for the hydrophobising effectobtained in carrying ou the method of the invention.

The fixer composition is buffered at a pH value from 7 to 12. Very oftenit is buffered at a pH of about 8-9. Hereby its stability isconsiderably improved. Any compound or-combination of compounds having abuffering action in the indicated pl-l region is suitable.-

Sodium' hydrogen carbonate and sodium tetraborate have proved to beespecially suited for this purpose as well as the following combinationsof compounds sodium carbonate and sodium hydrogen carbonate, sodiumcarbonate and citric acid, sodium carbonate, sodium hydrogen carbonateand citric acid, boric acid and sodium tetraborate, and trisodiumphosphate and oleic acid.

The compound or compounds for buffering the fixer may be applied in theusual concentrations generally known to those skilled in the art.

The fixer may comprise some further compounds'for improving thehydrophilic ink-repellent properties of the non-printing areas. Suitablesuch compounds are colloidal silica and hydrophilic colloid binders,hydro philic softening agents, inorganic acids and wetting agentsalready mentioned and exemplified above.

These compounds mostly are added to the fixer in a concentration rangingfrom about 5 to about 200g'per liter.

, The fixer may also contain compounds for improving the ink-receptivecharacter of the printing areas such as higher fatty acids, e.g. oleicacid, and hydrophobic softening agents, e.g., dimethyl phthalate,dibutyl phthalate, the phthalic acid ester with the following formulaThe fixer composition used in carrying out the method of the presentinvention is very stable to aerial oxidation and to temperaturefluctuations and it may be used for the production of many printingplates without having to frequently adjust the processing time. Manyprinting plates (about 100 plates of 21 cm X 29.7 cm size per liter offixer) can be produced before the fixer composition is fully exhausted.

At the moment the treatment with the aqueous fixer starts, the outercolloid layer showing the silver pattern may be in dry as well as in wetcondition. A superficial oxidationof the silver pattern suffices;generally, however, a more penetrating oxidation is advantageous.Generally, the treatment with the fixer does not last long, mostly nolonger than about seconds and can be accelerated by increasing theconcentration of the components present in the fixer. The plate may bestored for a long time before being fixed and even thereafter it may bestored for a long time before being used in the printing process.Preferably, however, the fixing step is carried out just beforeprinting.

Just as the development or activator liquid for the production of thediffusion transfer image the fixer can be applied in different ways,e.g., by spraying, by rubbing, with a lick roller, or by dipping thematerial to be treated in the liquid composition.

Also the fixing step of the printing plate may occur automatically byconducting the plate through a device having a narrow channel filledwith the fixer composition and at the end thereof between two squeezingrollers. In order to reduce the risk for aerial oxidation of the fixerto a minimum, funnel-shaped inand outlet openings may be provided at theends of the narrow channel and an upperlying plastic bag containing thefixer liquid may be used. If the apparatus is not used, the bag is moveddownwards and the fixer runs back from the channel into the bag.

aqueous phase are suitable too. In that case the aqueous phase maycontain thickeners or other usual compounds for improving thehydrophilic character of the non-printing areas of the lithographicprinting plate as described above. Suitable lacquers are described inthe United Kingdom Pat. specifications No. 967,598 filed Feb. 6, 1961 byKalle, 968,706 filed June 2, 1961 by Geva ert Photo-Producten N.V.,1,0,04,342 filed July 17, 1962 by Kalle, 1,071,163 and 1,071,164 bothfiled Apr. 30, 1964 by Gevaert Photo-Producten N.V. Resins that haveproved to be especially suitable for improving the ink-receptivecharacter of the printing areas and strengthening them arephenol-formaldehyde acid esters, epoxy resins e.g. condensation productsof a poly aryl ethylene oxide) with an acid anhydride, an amine oranother suitable compound and epoxidized polyesters.

The resin, wax or oil used mostly is present in a concentration of fromabout 100 to about 500 g per liter of liquid lacquer composition. Theliquid lacquer composition may be applied after the aqueous compositioncontaining. the oxidizing agent has been applied and while the printingplate is still wet. Only when an emulsion lacquer is used the plate neednot necessarily to be wet at the stage the lacquer is applied. Thelacquer may be applied by dipping, spraying, spreading or by means of amaterial soaked therewith. The lacquer is rubbed out, e.g., with a plugof wadding. The hydrophobic solid 1 substances settle on the image areasand improve the The production of the diffusion transfer silver image ontop of the photographic material (occasionally including the image-wiseexposure of the silver halide emulsion layer) and the treatment with thefixer may occur automatically, e.g., in processing stations as describedabove, and occasionally can be carried out both in a compact processingunitcomprising both processing stations.

After the application of the fixer the sheet material is ready for useas a printing plate. This means that no further treatment with a lacquercomposition for strengthening the printing parts is necessary.

This is an important advantage over most of the conventional methodshitherto used for the production of a planographic printing plate thatrequire the application of a lacquer as an essential feature.

Nevertheless, in some cases the hydrophobic character of theink-receptive parts may still be improved and their mechanical strengthmay be reinforcedby applying a lacquer thereon. Suitable lacquercompositions are solutions of oils, waxes and resins in organicsolvents. Suitable organic solvents are cyclohexanone, acetone, butanol,monomethyl ether of ethylene glycol, monethyl ether of diethyleneglycol, tetrahydrothiophene-l,l-dioxide, diacetone, dioxane,1,2-dichloroethane, ethyl acetate, trichloroethylene, butyl butyrate,diethanolamine and dimethylformamide. Mixtures of such organic solutionswith an aqueous phase or dispersions of such organic solutions in anhydrophobic ink-receptive character thereof. At the same time themechanical strength .of the printing areas is improved. The adherence ofthe lacquer to the printing areas may still be improved by heating theplate.

Instead of being applied by means of a separate aftertreatment of theprinting plate, the liquid lacquer composition may also be mixed with inthe aqueous composition containing potassium cyanoferrateflll') and theorganic compound for converting the silver image in a hydrophobicink-receptive pattern. The ratio of the organic phase that contains thehydrophobic solid substances to the aqueous phase then mostly iscomprised between H1 and H10.

The printing plate has to be wet at the stage the fatt printing ink isapplied. This is generally known in the art and it is usualto apply anaqueous liquid before applying the printing ink. This mayoccur by meansof a wet sponge or by means of the fountain arrangement of the printingmachine This wetting has to be more intensive as the printing plate ismore dry, e.g. when it has been stored for a long time after itsfixation and occasional lacquering.

The following examples illustrate the photographic material according tothe present invention-and the method of preparing a planographicprinting plate therewith.

EXAMPLE 1 To a paper support of g per .sq.m. a common high-sensitive,negative silver chlorobromide gelatin emulsion layer, hardened by meansof formaldehyde, was applied in such a way that an amount of silverhalide equivalent to 1 g of silver nitrate is'present per sq.m. Afterdrying of the silver halide gelatin emulsion layer, said layer wasovercoated at a rate of 20 g per sq.m with the following developmentnuclei composition water 890 ccs 12.5 aqueous saponin ccs aqueouscolloidal nickel sulphide dispersion comprising per 100 ccs 0.2 g ofnickel sulphide and 10 g of gelatin 7 100 ccs.

The photographic material thus obtained was exposed to an original andtreated for 30 sec. in the following processing composition sodiumhydroxide to g anhydrous sodium sulphite 75 g potassium bromide l ghydroquinone 16 g l-phenyl-3-pyrazolidinone 1 g water up to 1,000 ccsanhydrous sodium thiosulphate 10 g.

A diffusion transfer silver image was produced on top of the material. Y

The material was then rubbed for somev 20 seconds with a plug of waddingsaturated with the following fixer composition:

10% aqueous sodium carbonate 30 ccs 5 I: aqueous sodium hydrogencarbonate 30 ccs 10 1) aqueous citric acid 20 ccs potassiumcyanoferrateflll) 10.75 g 10 solution of compound (3) (l-ally)imidazolidine-Z-thione) in ethylene glycol monomethyl ether) 4 ccsdistilled water up to 100 ccs water 90 ccs glycerol 10 ccs colloidalsilica 2 ccs phosphoric acid 2 ccs EXAMPLE 2 To a paper support of 250 gper sq.m. a common high sensitive negative silver chlorobromide gelatinemulsion layer, hardened by means of formaldehyde and comprisinghydroquinone and 1 phenyl-3- pyrazolidone, was applied in such a waythat per sq.m

were present an amount of silver halide equivalent to 1 g of silvernitrate, 0.5 g of hydroquinone and 0.25 g of 1-phenyl-3-pyrazolidinone.

The light-sensitive material obtained was exposed image-wise and for 10sec. dipped. in the following processing liquid water 1,000 ccs sodiumphosphate-ll-water 75 g anhydrous sodium sulphite 40 g potassium bromide0.5 g anhydrous sodium thiosulphate 10 g aqueous colloidal nickelsulphide dispersion of example 1 In this way, a positive diffusiontransfer silver image was produced at the surface of the silver halideemul-. sion layer.

The material was then rubbed for some 15 seconds with a plug of waddingsaturated with the fixer described in example 1, wherein, however,compound (3) had been replaced by a same amount of compound (2). Theprinting plate thus prepared could be used for printing in the samemanner as described in example 1 and about the same good results wereobtained.

EXAMPLE 3 To a paper support of 135 g per sq.m a common high-sensitivesilver chlorobromide. gelatin emulsion layer comprising hydroquinone andl-phenyl-3- pyrazolidinone was applied in such away that per sq. m werepresent, an amount of silver halide equivalent to 1 g of silver nitrate,1 g of hydroquinone and 0.5 g of 1- phenyl-S-pyrazolidinone.

After drying of the silver halide gelatin emulsion layer, said layer wasovercoated at arate of g per sq.m with the followingcomposition water926 ccs gelatin 10 g 12.5 aqueous saponin 8 ccs 20 aqueous formaldehyde56 ccs Thenthe following liquid was applied in a proportion of 22 g persq.m

water 890 ccs 12.5 aqueous saponin 10 ccs aqueous colloidal nickelsulphide dispersion of example 1 100 ccs.

The photographic light-sensitive material obtained was exposedimage-wise and then guided through an automatic two-bath processingdevice, thehaths, of which had the following compositions respectively lactivating liquid) water a 1,000 ccs sodium phosphate-12-water 75 'ganhydrous sodium sulphite 40 g potassium bromide 0.5 g anhydrous sodiumthiosulphate 10 g H. The fixer described in example 1, wherein, however,compound (3) had been replaced by a same amount of compound (10).

The material obtained after this treatment was ready for use asplanographic printing plate with positive image values in respect of theoriginal. More than 1,000 copies could be printed therewith. Thefountain solution might be mere water or thefspecific fountaincomposition of example 1.

EXAMPLE 4 To an extra strong paper support of g per sq.m a thin grayantihalation layer was applied by pouring a dispersion of 3 g of lampblack in 1 liter of a 4'percent aqueous solution of gelatin at a rate of1 liter per 40 sq.m.

To this antihalation layer a common high-sensitive silver chlorobromidegelatin emulsion layer comprising hydroquinone andl-phenyl-3-pyrazolidinone was applied in such'a way that per sq.m therewere present an 20 ccs y al was guided through a processing amount ofsilver halide equivalent to 1 g of silver nitrate, l g of hydroquinoneand 0.5 g of l-phenyl-3- pyrazolidinone.

After drying, the silver halide gelatin emulsion layer was overcoated ata rate of 100 g per sq.m with the following composition water 926 ccsgelatin 10 g 12.5 aqueous saponin 8 ccs 20 aqueous formaldehyde 56 ccsThen the following liquid was applied at a rate of 22 g per sq.m

water 890 ccs 12.5 aqueous saponin 10 cos aqueous colloidal nickelsulphide 'nuclei dispersion comprising per 100 ccs 0.2 g of nickelsulphide and 10 g of gelatin 100 ccs.

water 1,000 ccs sodium phosphate-lZ-water 75 g anhydrous sodium sulphite40 g potassium bromide 0.5 g anhydrous sodium thiosulphate 10 gThereafter the multilayer material was kept for some 10 seconds in thedark in order to permit an intense diffusion transfer silver depositionto take place. A sharp bronzed legible diffusion transfer image becamevisible on a gray background. I

The plate was then moistened (e.g., by means of a plug of wadding) forsome 20 seconds with the following fixer composition:

16 aqueous sodium hydrogen carbonate 30 ccs potassium cyanoferrateflll)10.75 g solution of l-allyl-imidazolidine- 2-thione in ethylene glycolmonomethyl ether 4 ccs distilled water up to 100 ccs The pH-value ofthis buffered fixer composition amounted to 8.7. This fixer compositionwas very stable to aerial oxidation and to temperature fluctuations.With lliter thereof about 100 printing plates (21 cm X 29.7 cm size)could be prepared.

The preparation of the printing plate might occur automatically in acompact processing unit comprising the successive treating stations andwherein the plate was transported automatically from one unit to theother. v

The printing plate thus obtained was ready for use as a planographicprinting plate with positive image values in respect of the original. Itwas braced on a usual offset apparatus and after having been we'ttedwith water or another usual fountain solution (e .g., a liquid composedof 90 ccs of water, 10 ccs of glycerol, 2 ccs of colloidal silica and 2cos of phosphoric acid), the fatty printing ink was applied and printingstarted. More than 1,000 copies were printed with the plate thusprepared.

About the same good results could be obtained by replacing the fixercomposition described above by one of the following fixer compositions10 aqueous sodium carbonate 30 cos 5 aqueous sodium hydrogen carbonate30 ccs potassium cyanoferrateflll) 10.75 g 10 I: solution ofl-allyl-imidazolidine- 2-thione in ethylene glycol monomethyl ether 4ccs distilled water up to 100 ccs The pH-value of this buffered fixercomposition amounted to 10.2. I

10 aqueous sodium carbonate 30 ccs 10 aqueous citric acid 30 ccspotassium cyanoferrateflll) 10.75 g 10 solution ofl-allyl-imidazolidine- 2-thione in ethylene glycol monomethyl ether 4cos distilled water up to 100 ccs The pH-value of this buffered fixercomposition amounted to 7.9.

' lll.

10 aqueous boric acid 30 cos l0 aqueous sodium tetraborate 30 ccspotassium cyanoferrateflll) 10.75 g 10 solution ofl-allyl-imidazolidine- 2 -thione in ethylene glycol monomethyl ether 4cos distilled water up to ccs The pl'l-.value of this buffered fixercomposition amounted to 8.1.

10 aqueous sodium tetraborate 30 ccs potassium cyanoferrateflll) 10.75 g10 solution of l-allyl-imidazolidine- Z-thione in ethylene glycolmonomethyl ether 4 cos distilled water up to 100 ccs The pl-l-value ofthis buffered fixer composition amounted to 9.5.

water 50 ccs trisodium phosphate 4 g potassium cyanoferrateflll) 9.8 gethanol 26.2 ccs oleic acid 6.5 ccs 10 17 solution ofl-allyl-imidazolidine- 2-thione in ethylene glycol monomethyl ether 5.2ccs distilled water up to 100 ccs The pl-l-value of this buffered fixercomposition amounted to 7.3. V1. Same as V but the amount of oleic acidwas reduced to only 1 cc.

The pH-value of this buffered fixer composition amounted to l 1.2.

In case fixer V or V] is applied, the additional advantage of a stillimproved ink-receptivity of the printing parts of the printing plate istaken.

7 EXAM PLE 5 To a usual flexible film support of cellulose triacetate anantihalation backing was applied by pouring the following coatingcomposition at a rate of 1 liter per 20 sq.m

water 570 ccs gelatin 40 g 50 g of a red pigment dye (C.l. 15.865

Lake) in 300 ccs of water 12.5 1: aqueous saponin l ccs 20 aqueousformaldehyde l0 ccs EXAMPLE 6 A printing plate was prepared as describedin example 4, with the difference, however, that the gelatin layerdirectly on the silver halide emulsion layer was applied from thefollowing coating composition water 926 ccs gelatin 5.6 g 12 1: aqueoussaponin 8 ccs 20 k aqueous formaldehyde 56 ccs propylene glycol ester ofalginic acid 20 g A printing plate was still improved printingcharacteristics was obtained.

We claim:

1. A method of preparing a planographic printing plate from aphotographic sheet material comprising a light-sensitive silver halideemulsion layer and an exterior hardenable hydrophilic colloid stratumwhich comprises:

l. forming a pattern of finely divided silver particles at the exteriorsurface of said stratum by the steps of:

a. image-wise exposing said emulsion layer to light according to theimage to be printed,

b. contacting said stratum'with a liquid dispersion of insolubledevelopment nuclei for precipitating complexed silver halide as metallicsilver, to

deposit said nuclei at said surface of saidstratum, and c.photographically developing the exposed emulsion layer with an aqueousalkaline liquid in the presence of a photographic developing agent forsilver halide and a complexing agent for silver halide to form saidsilver particles at the free surface of said stratum by theprecipitation by said nuclei of migrating undeveloped complexed silverhalide;

2. contacting the developed material with an aqueous fixer compositioncontaining an oxidizing agent for metallic silver and an organic thioneor mercapto tautomer thereof for converting the pattern of silverparticles into a hydrophobic inkrecept ive' attern;and 3. chemical yhardening said colloid stratum at the latest before said material isused for printing, said hardening being at least sufficient. to preventtransfer of any substantial amount of such colloid during printing.

2. The process of claim 1 wherein said colloid stratum is hardened priorto contacting the same with said fixer composition.

3. The process of claim 1 wherein said colloid stratum is constituted bythe external surface stratum of said emulsion layer.

4. The process of claim 1 wherein said colloid stratum is a separatelayer arranged in superposed rela tion to said emulsion layer.

5. The process of claim 1 wherein said insoluble development nuclei aredispersed in said aqueous alkaline liquid for developing saidlight-sensitive emulsion layer. v

6. The process of claim 1 wherein said development nuclei aredispersedin a liquid applied to said colloid stratum prior to developing theemulsion layer with said aqueous alkaline liquid.

7. The process of claim 1 wherein said oxidizing agent is a metal salt.

8. In a method for the preparation of a planographic printing plateaccording to claim 1, wherein an antihalation dye or pigment layer isprovided for said emulsion layer.

9. In a method for the preparation of a planographic printing plateaccording to claim 1, wherein the support of the sheet material is atransparent hydrophobic film support.

10. In a method for the preparation of a planographic printing plateaccording to claim 4 wherein the 'hardenable hydrophilic colloid layerpresent on top of the silver halide emulsion layer is a gelatin layer.

1 1. In a method for the preparation of a planographic printing plateaccording to claim 1, wherein the hardening of the colloid stratum, isachieved by a hardener released by the application of the aqueousalkaline liquid. l

12. In a method for the preparation of a planographic printing plateaccording to claim 4, wherein the outer hydrophilic colloid layercontains a substantial amount of pigment particles homogeneouslydispersed therein.

2. The process of claim 1 wherein said colloid stratum is hardened priorto contacting the same with said fixer composition.
 2. contacting thedeveloped material with an aqueous fixer composition containing anoxidizing agent for metallic silver and an organic thione or mercaptotautomer thereof for converting the pattern of silver particles into ahydrophobic ink-receptive pattern; and
 3. chemically hardening saidcolloid stratum at the latest before said material is used for printing,said hardening being at least sufficient to prevent transfer of anysubstantial amount of such colloid during printing.
 3. The process ofclaim 1 wherein said colloid stratum is constituted by the externalsurface stratum of said emulsion layer.
 4. The process of claim 1wherein said colloid stratum is a separate layer arranged in superposedrelation to said emulsion layer.
 5. The process of claim 1 wherein saidinsoluble development nuclei are dispersed in said aqueous alkalineliquid for developing said light-sensitive emulsion layer.
 6. Theprocess of claim 1 wherein said development nuclei are dispersed in aliquid applied to said colloid stratum prior to developing the emulsionlayer with said aqueous alkaline liquid.
 7. The process of claim 1wherein said oxidizing agent is a metal salt.
 8. In a method for thepreparation of a planographic printing plate according to claim 1,wherein an antihalation dye or pigment layer is provided for saidemulsion layer.
 9. In a method for the preparation of a planographicprinting plate according to claim 1, wherein the support of the sheetmaterial is a transparent hydrophobic film support.
 10. In a method forthe preparation of a planographic printing plate according to claim 4wherein the hardenable hydrophilic colloid layer present on top of thesilver halide emulsion layer is a gelatin layer.
 11. In a method for thepreparation of a planographic printing plate according to claim 1,wherein the hardening of the colloid stratum is achieved by a hardenerreleased by the application of the aqueous alkaline liquid.
 12. In amethod for the preparation of a planographic printing plate according toclaim 4, wherein the outer hydrophilic colloid layer contains asubstantial amount of pigment particles homogeneously dispersed therein.